Flow Rate Converter
GPM, L/min, m³/h — three-way live converter.
How to use
Type a value in any of the three fields. The other two update live using exact conversion factors.
- Enter GPM, L/min, or m³/h.
- Reference the fixture table for typical flow rates (faucets, showers, washers).
- For pipe sizing, combine flow rate with allowable velocity (typically 8 ft/s for cold water, 5 ft/s for hot).
- Real plumbing sizing belongs to a licensed plumber working from the local plumbing code.
Reviewed 3 June 2026 · methodology cited
About this converter
Flow rate is the volume of water passing a point per unit of time. Plumbers and HVAC technicians work in three different units: US gallons per minute (GPM) for North American residential and light-commercial plumbing, litres per minute (L/min) for European and metric installations, and cubic metres per hour (m³/h) for larger commercial and industrial work.
This converter handles all three bidirectionally. The reference table below lists typical flow rates for common plumbing fixtures — useful for cross-checking a manufacturer spec sheet or a plumbing code fixture-unit calculation.
Conversion factors
The conversions are exact by definition: 1 US gallon = 3.785 411 784 L, and 1 hour = 60 minutes, so 1 GPM = 3.785 411 784 L/min = 0.227 124 7 m³/h.
Going the other way: 1 L/min = 0.264 172 GPM = 0.06 m³/h; 1 m³/h = 4.402 87 GPM = 16.666 67 L/min.
A worked example: a typical bathroom shower head at 2.5 GPM converts to 9.46 L/min or 0.568 m³/h. A garden hose at 5 GPM is 18.93 L/min. A 200 GPM commercial pump is 757 L/min or 45.4 m³/h. Note that GPM in this calculator means US gallons; Imperial (UK) gallons are larger by 20 percent (1 Imp gallon = 1.2 US gallons) and would give different numbers.
Typical fixture flow rates
| Fixture | GPM | L/min | Note |
|---|---|---|---|
| Bathroom faucet | 1.5 | 5.7 | Federal max |
| Kitchen faucet | 2.2 | 8.3 | Federal max |
| Shower head | 2.5 | 9.5 | Federal max |
| Garden hose (5/8″) | 5–9 | 19–34 | Depends on supply pressure |
| Toilet refill | 3 | 11.4 | Tank fill rate |
| Dishwasher | 1.5 | 5.7 | During fill cycle |
| Clothes washer | 4 | 15.1 | During fill cycle |
| Hose bib (3/4″) | 8–12 | 30–45 | Outdoor faucet |
| Tankless WH (whole home) | 4–10 | 15–38 | Depends on temperature rise |
| Fire sprinkler (one head) | 15–25 | 57–95 | NFPA 13 light hazard |
Sizing notes
US plumbing codes (UPC, IPC) limit fixture flow rates: 2.5 GPM for showerheads, 2.2 GPM for kitchen faucets, 1.5 GPM for bathroom faucets, 1.28 GPF for water-saving toilets (gallons per flush, not minute). These limits date from the Energy Policy Act of 1992 and have been tightened in several state codes since.
For pipe sizing, the standard approach pairs flow rate with allowable velocity. Cold water lines: maximum 8 ft/s (2.4 m/s). Hot water lines: maximum 5 ft/s (1.5 m/s) — higher velocities cause erosion-corrosion at fittings. Once you have flow rate (GPM) and pipe inside diameter (inches), velocity in ft/s is GPM × 0.4085 ÷ ID². Most plumbing codes also use fixture-unit tables that bake in the diversity factor — the assumption that not all fixtures will run at the same time — so the actual demand on a main line is much less than the sum of all fixture flow rates.
Frequently asked questions
GPM in US gallons or Imperial gallons?
This calculator uses US gallons. 1 US gallon = 3.785 L; 1 Imperial gallon = 4.546 L. The two systems differ by 20 percent. North American plumbing codes use US gallons; UK and some Commonwealth codes use Imperial. Always confirm which gallon you mean when reading a specification.
Why is shower flow limited to 2.5 GPM?
The US Energy Policy Act of 1992 set 2.5 GPM at 80 psi as the federal maximum for residential shower heads. Several state codes (California, Colorado, New York) tightened this to 2.0 or 1.8 GPM in the 2010s. The goal is reducing both water consumption and the energy required to heat hot water.
What is a "fixture unit"?
A fixture unit is a normalized demand value assigned to each plumbing fixture by the local code. It accounts for the diversity factor — the fact that not all fixtures run at once. The code provides a fixture-unit-to-GPM conversion table for sizing service lines and water meters. Fixture units are not in GPM and are not directly convertible.
Why distinguish hot and cold water velocity limits?
Hot water is more aggressive on copper pipes — it accelerates dezincification (in brass fittings) and erosion-corrosion at elbows and tees. The lower 5 ft/s limit for hot water extends pipe life. Cold water can run at 8 ft/s without significant erosion concerns over typical service lives.
Can I use this for irrigation sizing?
For unit conversion, yes. For sizing, no — irrigation has its own design methodology (Hunter graphs, distribution-uniformity considerations, head-to-head spacing) that this calculator does not address. Confirm with the irrigation design literature or an irrigation contractor.
Is m³/h the same as cubic metres per hour?
Yes — the same unit. European water-utility meters and industrial flowmeters quote in m³/h; the metric expression is identical to "cubic metres per hour."